| 1 | """Conversion pipeline templates.
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| 2 |
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| 3 | The problem:
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| 4 | ------------
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| 5 |
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| 6 | Suppose you have some data that you want to convert to another format,
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| 7 | such as from GIF image format to PPM image format. Maybe the
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| 8 | conversion involves several steps (e.g. piping it through compress or
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| 9 | uuencode). Some of the conversion steps may require that their input
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| 10 | is a disk file, others may be able to read standard input; similar for
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| 11 | their output. The input to the entire conversion may also be read
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| 12 | from a disk file or from an open file, and similar for its output.
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| 13 |
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| 14 | The module lets you construct a pipeline template by sticking one or
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| 15 | more conversion steps together. It will take care of creating and
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| 16 | removing temporary files if they are necessary to hold intermediate
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| 17 | data. You can then use the template to do conversions from many
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| 18 | different sources to many different destinations. The temporary
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| 19 | file names used are different each time the template is used.
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| 20 |
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| 21 | The templates are objects so you can create templates for many
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| 22 | different conversion steps and store them in a dictionary, for
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| 23 | instance.
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| 24 |
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| 25 |
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| 26 | Directions:
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| 27 | -----------
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| 28 |
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| 29 | To create a template:
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| 30 | t = Template()
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| 31 |
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| 32 | To add a conversion step to a template:
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| 33 | t.append(command, kind)
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| 34 | where kind is a string of two characters: the first is '-' if the
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| 35 | command reads its standard input or 'f' if it requires a file; the
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| 36 | second likewise for the output. The command must be valid /bin/sh
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| 37 | syntax. If input or output files are required, they are passed as
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| 38 | $IN and $OUT; otherwise, it must be possible to use the command in
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| 39 | a pipeline.
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| 40 |
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| 41 | To add a conversion step at the beginning:
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| 42 | t.prepend(command, kind)
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| 43 |
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| 44 | To convert a file to another file using a template:
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| 45 | sts = t.copy(infile, outfile)
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| 46 | If infile or outfile are the empty string, standard input is read or
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| 47 | standard output is written, respectively. The return value is the
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| 48 | exit status of the conversion pipeline.
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| 49 |
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| 50 | To open a file for reading or writing through a conversion pipeline:
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| 51 | fp = t.open(file, mode)
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| 52 | where mode is 'r' to read the file, or 'w' to write it -- just like
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| 53 | for the built-in function open() or for os.popen().
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| 54 |
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| 55 | To create a new template object initialized to a given one:
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| 56 | t2 = t.clone()
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| 57 | """ # '
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| 58 |
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| 59 |
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| 60 | import re
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| 61 | import os
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| 62 | import tempfile
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| 63 | import string
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| 64 |
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| 65 | __all__ = ["Template"]
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| 66 |
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| 67 | # Conversion step kinds
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| 68 |
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| 69 | FILEIN_FILEOUT = 'ff' # Must read & write real files
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| 70 | STDIN_FILEOUT = '-f' # Must write a real file
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| 71 | FILEIN_STDOUT = 'f-' # Must read a real file
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| 72 | STDIN_STDOUT = '--' # Normal pipeline element
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| 73 | SOURCE = '.-' # Must be first, writes stdout
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| 74 | SINK = '-.' # Must be last, reads stdin
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| 75 |
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| 76 | stepkinds = [FILEIN_FILEOUT, STDIN_FILEOUT, FILEIN_STDOUT, STDIN_STDOUT, \
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| 77 | SOURCE, SINK]
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| 78 |
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| 79 |
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| 80 | class Template:
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| 81 | """Class representing a pipeline template."""
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| 82 |
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| 83 | def __init__(self):
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| 84 | """Template() returns a fresh pipeline template."""
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| 85 | self.debugging = 0
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| 86 | self.reset()
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| 87 |
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| 88 | def __repr__(self):
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| 89 | """t.__repr__() implements repr(t)."""
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| 90 | return '<Template instance, steps=%r>' % (self.steps,)
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| 91 |
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| 92 | def reset(self):
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| 93 | """t.reset() restores a pipeline template to its initial state."""
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| 94 | self.steps = []
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| 95 |
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| 96 | def clone(self):
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| 97 | """t.clone() returns a new pipeline template with identical
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| 98 | initial state as the current one."""
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| 99 | t = Template()
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| 100 | t.steps = self.steps[:]
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| 101 | t.debugging = self.debugging
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| 102 | return t
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| 103 |
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| 104 | def debug(self, flag):
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| 105 | """t.debug(flag) turns debugging on or off."""
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| 106 | self.debugging = flag
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| 107 |
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| 108 | def append(self, cmd, kind):
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| 109 | """t.append(cmd, kind) adds a new step at the end."""
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| 110 | if type(cmd) is not type(''):
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| 111 | raise TypeError, \
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| 112 | 'Template.append: cmd must be a string'
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| 113 | if kind not in stepkinds:
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| 114 | raise ValueError, \
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| 115 | 'Template.append: bad kind %r' % (kind,)
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| 116 | if kind == SOURCE:
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| 117 | raise ValueError, \
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| 118 | 'Template.append: SOURCE can only be prepended'
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| 119 | if self.steps and self.steps[-1][1] == SINK:
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| 120 | raise ValueError, \
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| 121 | 'Template.append: already ends with SINK'
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| 122 | if kind[0] == 'f' and not re.search(r'\$IN\b', cmd):
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| 123 | raise ValueError, \
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| 124 | 'Template.append: missing $IN in cmd'
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| 125 | if kind[1] == 'f' and not re.search(r'\$OUT\b', cmd):
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| 126 | raise ValueError, \
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| 127 | 'Template.append: missing $OUT in cmd'
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| 128 | self.steps.append((cmd, kind))
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| 129 |
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| 130 | def prepend(self, cmd, kind):
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| 131 | """t.prepend(cmd, kind) adds a new step at the front."""
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| 132 | if type(cmd) is not type(''):
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| 133 | raise TypeError, \
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| 134 | 'Template.prepend: cmd must be a string'
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| 135 | if kind not in stepkinds:
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| 136 | raise ValueError, \
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| 137 | 'Template.prepend: bad kind %r' % (kind,)
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| 138 | if kind == SINK:
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| 139 | raise ValueError, \
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| 140 | 'Template.prepend: SINK can only be appended'
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| 141 | if self.steps and self.steps[0][1] == SOURCE:
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| 142 | raise ValueError, \
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| 143 | 'Template.prepend: already begins with SOURCE'
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| 144 | if kind[0] == 'f' and not re.search(r'\$IN\b', cmd):
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| 145 | raise ValueError, \
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| 146 | 'Template.prepend: missing $IN in cmd'
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| 147 | if kind[1] == 'f' and not re.search(r'\$OUT\b', cmd):
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| 148 | raise ValueError, \
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| 149 | 'Template.prepend: missing $OUT in cmd'
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| 150 | self.steps.insert(0, (cmd, kind))
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| 151 |
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| 152 | def open(self, file, rw):
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| 153 | """t.open(file, rw) returns a pipe or file object open for
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| 154 | reading or writing; the file is the other end of the pipeline."""
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| 155 | if rw == 'r':
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| 156 | return self.open_r(file)
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| 157 | if rw == 'w':
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| 158 | return self.open_w(file)
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| 159 | raise ValueError, \
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| 160 | 'Template.open: rw must be \'r\' or \'w\', not %r' % (rw,)
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| 161 |
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| 162 | def open_r(self, file):
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| 163 | """t.open_r(file) and t.open_w(file) implement
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| 164 | t.open(file, 'r') and t.open(file, 'w') respectively."""
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| 165 | if not self.steps:
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| 166 | return open(file, 'r')
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| 167 | if self.steps[-1][1] == SINK:
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| 168 | raise ValueError, \
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| 169 | 'Template.open_r: pipeline ends width SINK'
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| 170 | cmd = self.makepipeline(file, '')
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| 171 | return os.popen(cmd, 'r')
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| 172 |
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| 173 | def open_w(self, file):
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| 174 | if not self.steps:
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| 175 | return open(file, 'w')
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| 176 | if self.steps[0][1] == SOURCE:
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| 177 | raise ValueError, \
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| 178 | 'Template.open_w: pipeline begins with SOURCE'
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| 179 | cmd = self.makepipeline('', file)
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| 180 | return os.popen(cmd, 'w')
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| 181 |
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| 182 | def copy(self, infile, outfile):
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| 183 | return os.system(self.makepipeline(infile, outfile))
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| 184 |
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| 185 | def makepipeline(self, infile, outfile):
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| 186 | cmd = makepipeline(infile, self.steps, outfile)
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| 187 | if self.debugging:
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| 188 | print cmd
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| 189 | cmd = 'set -x; ' + cmd
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| 190 | return cmd
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| 191 |
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| 192 |
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| 193 | def makepipeline(infile, steps, outfile):
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| 194 | # Build a list with for each command:
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| 195 | # [input filename or '', command string, kind, output filename or '']
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| 196 |
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| 197 | list = []
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| 198 | for cmd, kind in steps:
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| 199 | list.append(['', cmd, kind, ''])
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| 200 | #
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| 201 | # Make sure there is at least one step
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| 202 | #
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| 203 | if not list:
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| 204 | list.append(['', 'cat', '--', ''])
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| 205 | #
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| 206 | # Take care of the input and output ends
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| 207 | #
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| 208 | [cmd, kind] = list[0][1:3]
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| 209 | if kind[0] == 'f' and not infile:
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| 210 | list.insert(0, ['', 'cat', '--', ''])
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| 211 | list[0][0] = infile
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| 212 | #
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| 213 | [cmd, kind] = list[-1][1:3]
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| 214 | if kind[1] == 'f' and not outfile:
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| 215 | list.append(['', 'cat', '--', ''])
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| 216 | list[-1][-1] = outfile
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| 217 | #
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| 218 | # Invent temporary files to connect stages that need files
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| 219 | #
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| 220 | garbage = []
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| 221 | for i in range(1, len(list)):
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| 222 | lkind = list[i-1][2]
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| 223 | rkind = list[i][2]
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| 224 | if lkind[1] == 'f' or rkind[0] == 'f':
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| 225 | (fd, temp) = tempfile.mkstemp()
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| 226 | os.close(fd)
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| 227 | garbage.append(temp)
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| 228 | list[i-1][-1] = list[i][0] = temp
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| 229 | #
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| 230 | for item in list:
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| 231 | [inf, cmd, kind, outf] = item
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| 232 | if kind[1] == 'f':
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| 233 | cmd = 'OUT=' + quote(outf) + '; ' + cmd
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| 234 | if kind[0] == 'f':
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| 235 | cmd = 'IN=' + quote(inf) + '; ' + cmd
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| 236 | if kind[0] == '-' and inf:
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| 237 | cmd = cmd + ' <' + quote(inf)
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| 238 | if kind[1] == '-' and outf:
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| 239 | cmd = cmd + ' >' + quote(outf)
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| 240 | item[1] = cmd
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| 241 | #
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| 242 | cmdlist = list[0][1]
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| 243 | for item in list[1:]:
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| 244 | [cmd, kind] = item[1:3]
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| 245 | if item[0] == '':
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| 246 | if 'f' in kind:
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| 247 | cmd = '{ ' + cmd + '; }'
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| 248 | cmdlist = cmdlist + ' |\n' + cmd
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| 249 | else:
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| 250 | cmdlist = cmdlist + '\n' + cmd
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| 251 | #
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| 252 | if garbage:
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| 253 | rmcmd = 'rm -f'
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| 254 | for file in garbage:
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| 255 | rmcmd = rmcmd + ' ' + quote(file)
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| 256 | trapcmd = 'trap ' + quote(rmcmd + '; exit') + ' 1 2 3 13 14 15'
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| 257 | cmdlist = trapcmd + '\n' + cmdlist + '\n' + rmcmd
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| 258 | #
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| 259 | return cmdlist
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| 260 |
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| 261 |
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| 262 | # Reliably quote a string as a single argument for /bin/sh
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| 263 |
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| 264 | # Safe unquoted
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| 265 | _safechars = frozenset(string.ascii_letters + string.digits + '@%_-+=:,./')
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| 266 |
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| 267 | def quote(file):
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| 268 | """Return a shell-escaped version of the file string."""
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| 269 | for c in file:
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| 270 | if c not in _safechars:
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| 271 | break
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| 272 | else:
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| 273 | if not file:
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| 274 | return "''"
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| 275 | return file
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| 276 | # use single quotes, and put single quotes into double quotes
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| 277 | # the string $'b is then quoted as '$'"'"'b'
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| 278 | return "'" + file.replace("'", "'\"'\"'") + "'"
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